As a technique of this type, heretofore, a rotation sensor has been widely used in various fields. For vehicle engines, a crank angle sensor which is one of rotation sensors is used to detect rotation speed and rotation phase of an engine. One example of this crank angle sensor is described in JP 2001-41092A.
A crank angle sensor using a magnetic pickup is known as a representative example of crank angle sensors. This sensor is mainly used in such a manner that the magnetic pickup constituted of a magnet and a coil is placed to face a gear-shaped magnetic member placed on a rotary shaft, and a clearance distance between the pickup and the magnetic member is changed to thereby output a voltage waveform from the magnetic pickup. A problem of this technique is in that the magnetic pickup has a limitation in sharpening of magnetic flux of a leading end and also the gear-shaped magnetic member has a limitation in the increase in the number of gear teeth, resulting in a limitation in angle resolution.
Furthermore, an optical rotary encoder is generally known as another technique of detecting rotation. One example thereof is described in JP 6(1994)-95798A. However, this optical rotary encoder using light has a problem that is affected by adhesion of contaminants. If a slit is made narrower to increase the resolution, the slit is liable to be obstructed by contaminants. It is therefore difficult to use the optical rotary encoder in hostile environments in which it is apt to be exposed to oil, dust, and others.
Hence, there is an electromagnetic induction type rotary encoder capable of utilizing changes in magnetic field, differently from the optical type, to avoid the problem with contaminants. One example thereof is described in JP9(1997)-170934A. This type of electromagnetic induction type rotary encoder includes a magnet fixed to a rotary body and a plurality of coil patterns placed to face the magnet and arranged to detect the passage of the magnet in association with the rotation of the rotary body. Those coil patterns are arranged so that their phases are electrically displaced in a coil pattern area on a printed circuit board.